The deposition of organic contaminants on process equipment, screens, and containment vessels in papermaking can significantly reduce process efficiency and paper quality. Deposits on machine wires, felts, foils, headbox surfaces, screens, and instruments can result in costly downtime for cleaning to avoid the problems associated with poor process control, reduced throughput, and substandard sheet properties. Such contaminants are generically referred to in the paper industry as either “pitch” or “stickies”. Pitch deposits generally originate from natural resins present in virgin pulp, including terpene hydrocarbons, rosin/fatty acids or salts thereof, such as pimaric acid, pinic acid and abietic acid, glyceryl esters of fatty acid, sterols, etc. Stickies and white pitch generally refers to the hydrophobic substances used in the manufacture of paper such as sizing agents, coating binders, and pressure sensitive or contact adhesives. Such substances can form deposits when reintroduced in recycled fiber systems. Other common organic contaminants that are chemically similar to stickies and found in recycle applications include wax, which originates primarily from wax-coated old corrugated containers, and polyisoprene. Pitch and stickies may also contain entrapped inorganic materials such as talc, calcium carbonate, or titanium dioxide.
Recycled fiber also refers to secondary fibers which are repulped to provide the papermaking furnish with raw material for the production of new papers. The secondary fibers may be either pre-consumer or post-consumer paper material that is suitable for use in the production of paper products. Sources of secondary fiber may include old newspaper (ONP), old corrugated containers (OCC), mixed office waste (MOW), computer printout (CPO), ledger, etc. These once-processed papers contain various types of adhesives (pressure sensitive, hot melts, etc.), inks, and coating binders.
Pitch and stickies are hydrophobic in nature and thus unstable as colloids in aqueous papermaking environments, thereby facilitating their deposition. The major problems arising from deposition are as follows: (1) reduced throughput due to plugging of forming fabrics and press felts (2) sheet holes or paper breaks due to large deposits breaking loose from the equipment, and (3) reduced sheet quality due to large particle contaminants incorporated in the final sheet.
Surfactant additives are often used to disperse pitch and stickies, but current products have limitations. For example, cationic polymer dispersants can be easily attracted to fiber surfaces, which may reduce their effectiveness, and they may further interfere with the charge dynamics of fibers, which may lower the effectiveness of other additives such as strength agents. Anionic polymer dispersants may cause precipitation problems with wet strength agents or inorganic components. Nonionic surfactants such as nonylphenol ethoxylates may cause foaming issues which can upset the system. Accordingly, improved methodologies for controlling contaminant deposition in the papermaking process are needed.